The present inventive concept relates to photolithographic exposure equipment used in the manufacturing of semiconductor devices, LCDs and the like. More particularly, the present inventive concept relates to a photomask of photolithographic exposure equipment.
The manufacturing of electronic and optical devices, such as semiconductor devices and LCDs, includes a photolithography process in which the image of a very fine pattern such as a circuit pattern is transferred from a photomask to a substrate of the device under manufacture. An example of the substrate is a semiconductor wafer. To this end, exposure equipment is used. The exposure equipment is made up of several optical systems and thus, the equipment must possess high a degree of resolution to focus a precise image of the pattern of the photomask onto the wafer. Moreover, this process of transferring a pattern to a wafer is repeated many times on different areas (referred to as “shots”) of the wafer during a mass production process of, for example, manufacturing semiconductor chips. Therefore, various optical components, such as the photomask, a lens, and an aperture, etc., of the optical systems must offer a high degree of optical performance on a consistent and regular basis so that a critical dimension (CD) of a pattern in a particular shot is uniform and the CD is uniform from shot to shot.
The photomask is an optical component that bears the pattern whose image is to be transferred to the substrate of the electronic/optical device under manufacture. In addition, the photomask may have other patterns such as a blind pattern that enhances the precision of the optical transfer of the image to the substrate. A pellicle is attached to the photomask to protect the photomask. Furthermore, the maintaining of photolithographic exposure equipment entails cyclically removing the pellicle attached to the photomask, cleaning the photomask, and attaching a new pellicle to the photomask. Over time, however, such procedures reduce the thickness of the blind pattern of the photomask. In this case, the transmittance of the photomask increases, which causes a drop in shot uniformity on the wafer or other substrate.